The present invention relates to a NEW-TAB (Tape Automated Bonding) technology and a UFPL (Ultra Fine Pattern Lead-flame) technology, and particularly to an electronic parts mounting board suitable for a multilayer wiring board (buildup board) to be mounted on portable terminal devices, portable telephones, etc., and a method of producing the electronic parts mounting board.
Recently, in an information communication field, portable telephones, portable game devices, etc. having various functions in addition to a communication function have come to be frequently used along with development of multi-media. These portable terminal devices, etc. often use multilayer wiring boards on each of which a large number of electronic parts and wiring patterns for realizing a communication function, an information retrieving function, etc. are mounted.
Such a multilayer wiring board has required lightweightness and miniaturization, and has used an organic board having copper foils on both surfaces as a base board. The organic board is obtained by coating a glass fiber cloth called a glass epoxy prepreg with a semi-hardened epoxy resin.
A method of producing a multilayer board using such an organic board having copper foils on both surfaces includes the steps of coating the copper foils on both surfaces of the organic board with a resist and patterning the resist, removing an unnecessary copper foil by etching using the resist patterns as a mask, to form wiring patterns, forming contact holes passing through the organic board at specific positions of the wiring patterns, burying the contact holes with copper by electroless copper plating, and connecting the wiring patterns on both the surfaces to each other through the contact holes. The wiring board thus obtained is bonded to another wiring board obtained in the same manner by means of a thermosetting insulating member, to obtain a multilayer wiring board.
The multilayer wiring board using the organic board having copper foils on both the surfaces, however, has problems. Since the thickness of the prepreg is large, the finish thickness of the wiring board becomes large as the number of stacked layers of the wiring board becomes large. Further, since contact holes are formed by using a drill, diameters of the contact holes become large and the contact holes occupy large areas, to thereby obstruct higher density mounting, and a relative positional relationship between the contact holes is varied. Even if the contact holes are formed by laser beam drilling, an expensive equipment investment is required.
To solve such a problem, a buildup board production technology has been developed for reducing sizes, weights and costs of multilayer wiring boards. This board production technology is classified into the following four types:
(1) Photo Via Process
This process is carried out by preparing a core member for an inner layer, on both surfaces of which wiring patterns have been formed, forming a photosensitive insulating resin layer on both the surfaces of the core member, patterning the resist by photolithography, to form a resist mask, forming openings (via-holes) reaching the wiring patterns at specific positions using the resist mask, burying the openings with copper by copper plating, thereby forming electrodes (through-holes) for connection. With this process, the openings can be collectively formed by photolithography, it is possible to enhance a relative positional accuracy between the openings, and to shorten the contacts and form relatively small openings at a high resolution.
(2) First Laser Via Process
This process is carried out by preparing a core member for an inner layer, on both surfaces of which wiring patterns have been formed, forming a thermosetting insulating resin layer on both the surfaces of the core member, curing the thermosetting resin, forming openings (blind via-holes) reaching the wiring patterns at specific positions by laser beam drilling, and burying the openings with copper by copper plating, thereby forming electrodes (through-holes) for connection. With this process, since the blind via-holes are formed by laser beam drilling, the wiring board is less affected by contamination, and thereby the works in a clean room can be eliminated.
(3) Second Laser Via Process
This process is carried out by preparing a core member for an inner layer, on both surfaces of which wiring patterns have been formed, adhesively bonding copper foils, each of which is coated with a thermosetting insulating resin, on both surfaces of the core member, curing the thermosetting insulating resin, forming openings (blind via-holes) reaching the wiring patterns through the copper foils at specific positions by laser beam drilling, and burying the openings with copper by copper plating, thereby forming electrodes (through-holes) for connection.
With this process, since the blind via-holes are formed by laser beam drilling, the same advantage as that obtained by the first laser via process can be obtained, and since irregularities of the core member are buried in the thermosetting insulating resin, there can be obtained advantages that a multilayer wiring board having a larger number of layers can be easily obtained because of no irregularities of each core member, and that an adhesive force between the core members can be improved.
(4) Buried Bump Interconnection Technology Process
FIG. 3 is a sectional view showing a configuration example of a related art multilayer wiring board. A multilayer wiring board 10 shown in FIG. 3 is formed by a buried bump interconnection technology process. The multilayer wiring board 10 includes a core member 1 having wiring patterns 3A to 3C on the back surface and electrodes 2A to 2C for connection on the inner layer side. Bump electrodes 4A to 4C are provided on the electrodes 2A to 2C of the core member 1, respectively. A thermosetting insulating resin layer 5 is provided on the core member 1 in such a manner as to insulate the bump electrodes 4A to 4C. Circuit electrode patterns 6A to 6C are provided on the thermosetting insulating resin layer 5 and the bump electrodes 4A to 4C, respectively.
The bump electrodes 4A to 4C are formed by overprinting (bump-printing) copper-containing conductive paste at specific positions of a copper foil 2 shown in FIG. 4A in a state before the circuit electrode patterns 6A to 6C are formed, to form conical conductive paste portions 4Axe2x80x2 to 4Cxe2x80x2, curing the conical conductive paste portions 4Axe2x80x2 to 4Cxe2x80x2, superimposing the core member 1, the thermosetting insulating resin layer 5, and the copper foil 2 with the conical conductive paste portions 4Axe2x80x2 to 4Cxe2x80x2 as shown in FIG. 4B, and hot-pressing them in such a manner that the conical conductive paste portions 4Axe2x80x2 to 4Cxe2x80x2 pass through the thermosetting insulating resin layer 5 and reach the electrodes 2A to 2C of the core member 1, respectively. With this process, it is possible to eliminate the work of forming openings for connection, enhancing a relative positional accuracy between the contacts, and shortening the contacts.
The above-described related art buried bump interconnection technology process, however, has a problem. The conical conductive paste portions 4Axe2x80x2 to 4Cxe2x80x2 must be formed by bump-printing the conductive paste on the copper foil 2 in order to form the bump electrodes 4A to 4C. At this time, since the conductive paste must be overprinted, variations in widths and heights of the conductive paste portions may become large. As a result, it is difficult to form contacts having small diameters due to the limited accuracy of bump printing, thereby obstructing higher density mounting of a multi-layer wiring board. In addition, the other three processes have the following problems:
According to the photo via process, since the via-holes are formed by photolithography, the board is liable to be affected by contamination at the time of exposure, and therefore, the process must be performed in a controlled environment such as a clean room. Also, since the core member is coated with the photosensitive insulating resin, irregularities of the core member remain, so that it is difficult to accurately form a final pattern. Further, since the wiring patterns are formed only by subjecting the photosensitive insulating resin to copper plating, adhesive forces of the wiring patterns are weak.
According to the first and second laser via processes, since the blind via-holes are sequentially formed by laser beam drilling, a relative positional accuracy between the openings is reduced, and the contacts become short. Also, in the first laser via process, since the core member is coated with the thermosetting insulating resin, the irregularities of the core member remain, so that it is difficult to accurately form a final pattern. Further, since the wiring pattern is formed only by subjecting the photosensitive insulating resin to copper plating, adhesive forces of the wiring patterns are weak.
According to the second laser via process, since the openings reaching the wiring patterns are formed through the copper foils by laser beams, large energy beams are required, so that the work of forming openings having small diameters is complicated and an expensive laser beam drilling system is required.
In the above four processes, since circuit electrode patterns are formed by etching the copper foil, there is a limitation to finish accuracy of the wiring patterns, and therefore, in the case of applying the multilayer wiring board for a high frequency circuit, a special countermeasure such as impedance matching must be taken.
An object of the present invention is to provide an electronic parts mounting board capable of connecting circuit electrode patterns to a specific electrode circuit base member via small contacts comparable to those obtained by the photo via process at a high positional accuracy, and improving the flatness and adhesive force of the circuit electrode patterns, without use of an expensive laser system for drilling, and to provide a method of producing the electronic parts mounting board.
To achieve the above object, according to a first aspect of the present invention, there is provided an electronic parts mounting board including: an electrode circuit base member having an electrode on a surface of at least one side; a projecting electrode bonded to the electrode of the electrode circuit base member; an insulating member provided on the electrode circuit base member in such a manner as to insulate the electrode of the electrode circuit base member and the projecting electrode; and a circuit electrode pattern provided on the insulating member and the projecting electrode; wherein the projecting electrode is formed by forming a specific projecting conductive member at specific positions of the circuit electrode pattern by plating, and pressing the projecting conductive member into the insulating member so as to pass through the insulating member and reach the electrode of the electrode circuit base member.
With this configuration, since the circuit electrode pattern can be substantially integrated with the projecting electrode, and the projecting electrode thus integrated with the circuit electrode pattern can be bonded to the electrode of the electrode circuit base member, it is possible to provide an electronic parts mounting board having an electrode connection structure with a contact resistance almost negligible.
Since the irregularities such as the electrodes of the electrode circuit base member and the circuit electrode pattern can be buried in the insulating member, it is possible to provide an electronic parts mounting board of a very thin type which is excellent in flatness and adhesive force and is capable of increasing the mounting density. Such an electronic parts mounting board can be sufficiently applied to portable telephones and the like.
According to a second aspect of the present invention, there is provided a method of producing an electronic parts mounting board, including the steps of: forming a specific circuit electrode pattern on a surface of one side of a conductive base member to be plated and etched, by plating a specific conductive material thereon; selectively forming a non-plated material on the circuit electrode board on which the circuit electrode pattern has been formed; forming a projecting electrode for connection on the circuit electrode pattern by plating a specific conductive material on the circuit electrode pattern with the non-plated material used as a mask; after removing the non-plated material, putting an insulating thermal bonding member between the circuit electrode board and a specific electrode circuit base member, pressing the projecting electrode of the circuit electrode board into the thermal bonding member so as to reach the electrode circuit base member, to bond the circuit electrode board to the electrode circuit base member; and removing the conductive base member from a multilayer board obtained by bonding the circuit electrode board to the electrode circuit base member by selective etching.
With this configuration, blind contacts having small diameters comparable to those obtained by the photo via process can be obtained at a high relative positional accuracy without use of an expensive laser system for drilling, and the adhesive forces between the circuit electrode patterns and the projecting electrodes can be also significantly improved.
Since the conductive base member used as the temporary board is removed by overall etching from the multilayer wiring board obtained by bonding the circuit electrode board to the electrode circuit base member, it is possible to produce an electronic parts mounting board excellent in flatness and adhesive force and hence to sufficiently keep up with mass-production of electronic parts mounting boards such as buildup boards having blind contacts located at a high relative positional accuracy.